getDocIdSet

context - a AtomicReaderContext instance opened on the index currently
searched on. Note, it is likely that the provided reader info does not
represent the whole underlying index i.e. if the index has more than
one segment the given reader only represents a single segment.
The provided context is always an atomic context, so you can call
AtomicReader.fields()
on the context's reader, for example.

a DocIdSet that provides the documents which should be permitted or
prohibited in search results. NOTE:null should be returned if
the filter doesn't accept any documents otherwise internal optimization might not apply
in the case an emptyDocIdSet is returned.